| As a fruit tree in rose family (Rosaceae) and apricot genus (Prunus Linn.), apricot (Prunus armeniaca Linn.) has already been taken as one of the main resources for rural economy. Since blooming early in spring, it is often injured by late frost, and yield loss induced by frost at blooming period was 30%-40% almost every year, or sometimes there will be no production at all. Because of this quite serious loss, frost has already been one of the critical restricting factors in the cultivation and development of apricot. And this problem has not been resolved effectively. In order to clarify the mechanism of frost injury to apricot, to provide theory basis and probe new ways for effective frost provention,diferent apricot cultivars were used as materials to study the changses of supercooling points at different developmental stages, effects of low temperature on cold resisitence, pollination in floral organs, effects of comprehensive measures on cold resisitence in floral organs, and frost-controlling efficacy of bactericides. The main results of the sduty are as follows:1. The cold resisitentce of apriot flowers were in relationship with those development stages. The results showed that, with the development of flower buds, SCP and FP in five apricot cultivars increased. Young fruits were mostly sensitive to frost, while at blooming period floral organs were sensitive to frost; among three florlal organs, the lowest SCP and FP were in petal, then stamen and pistil. SCP in stamen and pistil were 1℃～2℃higher than that in petal; The order of cold resistence among cultivars was Youyi>Longwangmao>Honghebao>Golden sun>Katy.2. The effects of low temperature on antioxidant defence systems, osmolytes contents, and hormone contents were showed as follows:Compared with control, O2.—genaration rate H2O2 concentrations, MDA concentrations of apricot floral organs under different low temperatures were in increasing trends, and the order of floral organs in three index were all taken as petal>stamen>pitil; Activities of SOD, GPX, CAT, APX, GR, DHAR, MDHAR were in the trend of increasing firstly, and then decreasing, while different enzyme activities varied with floral organs, which indicated that different floral organs depented on different antioxidant enzymes to eliminate ROS for frost precention. Antioxidant concentrations were increased firstly and then decreased, but DHA concentration was excepted. The temperature at which antioxidant concentrations were the highest varied with floral organs. In addition, low temperature duration increased relative electrolytic leakage and MDA concentrations in floral organs of apricot, which indicated that the damage induced by low temperature and its duration was in similar to low temperatures.With temperature decreasing, soluble protein, soluble sugar and pro-aa contents of floral organs increased, while contents were different among floral organs, which maybe in relation to pollination beside saturation modulation.Hormone were in relation to cold resisitance of apricot floral organs, while hormone type varied with the changes of temperature, and hormone concentrations were difference among floral organs. Concentrations of IAA and ABA were the highest in petals, but GA and Z+ZR concentrations were the highest in pistils. The ratio of ABA/GA, ABA/IAA and ABA/Z+ZR were behaved as petal>stamen>pistil, which indicated that cold resisitance did not rest on a certain hormone, but the ratio among hormones. ZT was not examined in apricot floral organs.3. Low temperature affected pollination biology of apricot, the results showed that: low temperature decreased the pollen activity, pollen germination, and pollen tube length of apricot, but the effect of low temperature treatment on pollen activity of different cultivars was diversity. The stylars treated with -2℃or -3℃after pollination for 4h and 24h respectively were examed using fluorescence microscope, the results showed that low temperature restrained the development of pollen tube, and stopped those development in stylar forwardly, while the damage degree of low temperature to pollen tube in pollinated stylar varied with development period, it showed that the effect of low temperature on pollen germination 4h after pollination was significant than that 24h after pollination.4. The development of peripheral branches, soil properties and cold resisitence of floral organs were studied after using comprehensive cultural measures, the results showed that, comprehensive cultural measures promoted the peripheral branches 30.50cm longer and 0.52cm thicker than its controls, increased the photosynthetic rate of leaves, the ratio of effective flower, and fruit set percentage, and enhanced apriot kernel/fruit apriot and kernel quality. The comprehensive cultural measures improved soil properties, enhanced the amount of microorganism in soil, promoted activities of correlative enzymes,such as invertase,protease. This cultural measure caused fibres development by increasing the amount of fibres at layer of 0cm-30cm, 30cm-60cm, 60cm-90cm by 2.17, 1.17,1.56 times respectively, compered with control. In addition, Comprehensive cultural measures decreased SCP, cell membrane permeability significantly, and MDA concentrations of Longwangmao, improved activity of SOD and POD, concentrations of soluble protein and pro-aa significantly, decreased frost injury index of floral organs, thus cold resistance of apricot floral organs were improved. 5. Five out of nine bactericides,labeled as No.1, No.2, No.3, No.5, and No.7, were selected for eradicating INA bacteria and destroying ice-nucleation protein by means of vali and culture on medium containing INA bacteria. The effects of selected bactericides were investigated on preventing frost damage in solar greenhouse and field. The results indicated that when frost occurred at -4℃in solar greenhouse, both No.3 and No.7 were most effective among the five bactericides with frost-controlling efficacy being 47.05%~67.74% and 49.44%~69.33%, respectively, and No.3 and No.7 increased percentage of fruit set by 12.25%~14.83% and 4.69%~11.36%, respectively, as compared with control. In filed experiment, the frost-controlling efficacy of No.3 was 21.80% at -6.5℃, and it significantly decreased the percentage of fruit set by 9.17%. |
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